GEOL 446 Environmental Geology

1. GEOL 446Environmental Geology PART I FOUNDATIONS OF ENVIRONMENTAL GROLOGY Chapter 1: philosophy and Fundamental Concepts Chapter 2: Earth Material and Processes Chapter 3Soils and Environment

2. 3. Soils and the Environment Soil is one of the most important earth materials we encounter each day, but the definition of soil is difficult. Soil Scientists (and most ordinary people): • fine-grained, well-weathered earth material that is able to support plant growth • focus on the physical and chemical properties Engineers: • any earth material that can be removed without blasting • focus on particle size and the amount of organic material • engineering applications

3. 3. Soils and the Environment Environmental Geologists: • must understand soil from many perspectives • characteristics affect agriculture, engineering, hydrology, natural hazards and other aspects of land use • soil development and soil character is crucial to good land use planning. • Read Table 3.1 (Soil Taxonomy) • Understand the meaning of soil types, but do not memorize • all of them. • Read Table 3.2 (Unified Soil Classification) • Learn the definition of each constituent that makes up soil.

4. Soil Development Soil is an important part of the geologic cycle and soil characteristics are influenced by parent material, climate, topography, weathering, and the amount of time a particular soil has had to develop. As soil develops, weathering creates distinct layers in soil. We call these layers soil horizons, and each soil horizon has distinctive characteristics. Every soil has a soil profile, a list of the horizons that describe a particular soil.

5. Soil Rock Soil Horizons Materials in a Soil System: Vertical and horizontal movements create a soil profile made up of distinct layers parallel to the surface, which are called soil horizons. Organic top layer (O) Zone of leaching (A and E) Zone of accumulation (B) Rock (weathered & unweathered) (C and R)

6. Soil Horizons O Mostly organic materials, decomposing leaves, and twigs. Often dark brown color. A Mineral and organic materials, light black to brown. Leaching of clay, Fe and Ca. E Light colored materials due to leaching of clay, Ca, Mg, and Fe to lower horizons. Horizons A and E make up the Zone of Leaching. B Enriched in clay, Fe oxides, Silica, carbonate and other material leached from above. This is the Zone of Accumulation. C Partially altered (weathered) parent material, which is either rock or loose sediment. RUnweathered (unaltered) parent material = rock. ~3m

7. Soil Development • A soil’s profile depends on its age and its conditions of formation. Soil profile is the primary criteria for soil classification. • Soils can be compared in terms of their relative development. Weakly developed soil profiles are generally younger and may have fewer horizons; well-developed soils are generally older and have more horizons. Chronosequences • Relative development of a series of soils allows their arrangement in a soil chronosequence. A soil chronosequence gives information about the history of the landscape. The relative development of the soils in a chronosequence tells the investigator about the climate and depositional history of the area.

8. Soil Texture Texture = relative proportion of sand, silt and clay. Texture classes: Coarse sands, loamy sand and sandy loams with less than 18 % clay, and more than 65 % sand. Medium sandy loams, loams, sandy clay loams, silt loams with less than 35 % clay and less than 65 % sand; the sand fractions may be as high as 82 % if a minimum of 18 % clay is present. Fine clays, silty clays, sandy clays, clay loams and silty clay loams with more than 35 % clay.

9. 100 % CLAY See Figure 3.2 in textbook Clay Clay (%) Silt (%) Clay loam Loam 100 % SILT Sandy loam Silt loam Sand Silt 100 % SAND Sand (%)

10. Soil Classification Soils are often referred to as being sandy or clayey, or silty. Different countries use different standards to define sand particle and silt particle sizes. Particle sizes Gravel, Cobbles, and Boulders particles greater than 2 mm diameter Coarse and medium sand particles from 2 mm to 0.2 mm diameter Fine and very fine sand particles from 0.2 mm to 0.074 mm diameter Silt particles from 0.074 mm to 0.004 mm diameter Clay particles less than 0.004 mm diameter

11. Soil Classification WELL SORTED WELL GRADED

12. Unified Soil Classification System GW = well-graded gravel GP = poorly graded gravel GM = silty gravel GC = clayey gravel SW = well-graded sand SP = poorly graded sand SM = silty sand SC = clayey sand ML = silt MH = micaceous silt OL = organic silt CL = silty clay CH = high plastic clay OH = organic clay PT = peat and muck Clean (<5 % fines) Dirty (>12 % fines) Clean (<5 % fines) Dirty (>12 % fines) Non-plastic Plastic >50 % larger than 0.074 mm FINE-GRAINED COARSE-GRAINED Clays Silts Sands Gravels >50 % smaller than 0.074 mm Mostly Organics

13. Water in Soils Types of water: Water on Earth is known by different terms, depending on where it is and where it came from. • Meteoric water = water in circulation. • Connate water = "fossil" water, often saline. • Juvenile water = water from the interior of the earth. • Surface water = water in rivers, lakes, oceans, etc • Subsurface water = groundwater, connate water, soil, capillary water. • Groundwater in the zone of saturation, may be fresh or saline.

16. Water in Soils Moisture Content of soil is calculated as follows: W = weight, so that: [(Wwet - Wdry)/Wdry] x 100 = H2O content (%) Moisture content affects the engineering properties and stability of soils. A soil that is stable in dry conditions may become unstable to support the structures built on it when saturated with water.

17. Engineering Properties of Soils Plasticity • related to the water content Liquid Limit (LL) • water content above which the soil behaves like a liquid Plastic Limit (PL) • water content below which the soil is no longer plastic Plasticity Index (PI), PI = LL - PL • range of water contents that make the soil behave as a plastic material • Low PI (5 %):small change in water content, soil changes from solid to liquid • High PI (> 35%): potential to expand and contract on wetting and drying

18. Engineering Properties of Soils Expansive Soils • high content of swelling clay (montmorillonite) • soils swell when water is incorporated between clay plates • shrinking occurs when soil is dried • damage to building and road foundations Study Table 3.3in textbook to understand more about soil descriptions and their significant properties. • Study the Universal Soil Loss Equation(erosion) : A = RKLSCP

19. Universal Soil Loss Equation • A = RKLSCP A = long-term average annual soil loss for the site R = long-term rainfall runoff erosion factor K = soil erodibility index L = hillslope/length factor S = hillslope/gradient factor C = soil cover factor (crop/vegetation and mgmt. factor) P = erosion-control practice factor • Used to predict the impact of sediment losson local streams and other resources and to develop managementstrategies for minimizing impact.

20. FOREST Precipitation Evapotranspiration Interception Soil Water infiltrates and runs through soil Rock Water in Soils

21. Water in Soils Farming Precipitation Less Interception and Evapotranspiration Soil Increased surface runoff and soil erosion from freshly plowed land Rock Increased sediment in channel

22. Water in Soils CLEARCUT Precipitation Little Interception and Evapotranspiration Soil compaction Increased surface runoff and sediment; weaker soil Rock More sediment in channel

23. URBANIZATION Precipitation Soil Large increase in runoff from urban surfaces and storm sewers Rock Water in Soils

24. Key Terms to Review: • weathering • soil horizons • soil profile development • soil chronosequence • soil fertility • unified soil classification • soil strength • soil sensitivity • liquefaction • compressibility • erodibility • permeability • corrosion potential • shrink-swell potential • expansive soils • soil pollution • desertification • water table • soil plasticity index